Wetlands occupy only a small part of the landscape that is now the conterminous United States percent in and just 5 percent in Dahl and others, Nonetheless, they are important to birds. During the past 20 years, policies and programs that encourage altering, draining, or filling of wetlands have decreased, and policies that encourage wetland conservation and restoration have increased. See article "Wetland Protection Legislation" in this volume. Among the wetland attributes society seeks to protect and conserve are those that benefit wildlife, particularly migratory birds.
This article discusses the benefits that wetlands provide for birds and the effects of wetland losses on birds. The value of a wetland to a specific bird species is affected by the presence of surface water or moist soils and the duration and timing of flooding. Water might be present during the entire year, during only one or more seasons, during tidal inundation, or only temporarily during and after rainfall or snowmelt. At times water might not be present at the land surface, but might be close enough to the land surface to maintain the vegetation and foods that are needed by birds.
Birds may use wetlands located in depressions in an otherwise dry landscape, along streams, or in tidally influenced areas near shorelines. Wetlands provide food for birds in the form of plants, vertebrates, and invertebrates. Some feeders forage for food in the wetland soils, some find food in the water column, and some feed on the vertebrates and invertebrates that live on submersed and emergent plants. Vegetarian birds eat the fruits, tubers, and leaves of wetland plants.
Water temperatures influence food production. Invertebrate production in the water column may ultimately depend on water temperature and the ability of a wetland to produce algae.
Cold water might not be a hospitable environment for small animals and plants that some wetland birds eat. However, water that is too warm also might not produce foods that some birds prefer. Many bird species use forested wetlands as well as forested uplands, feeding on the abundant insects associated with trees fig. These birds are not dependent on wetlands because they use both habitats equally well. Some birds, such as wood ducks, are found primarily in forested wetlands and are dependent on this wetland type.
Many migratory birds are wetland dependent, using wetlands during their migration and breeding seasons. Migratory birds may spend the winter in wetlands in the Southern United States, or farther south fig.
Throughout winter, these birds use southern wetlands for food and nutrients to sustain them for their return trip north and the breeding season. Considerable research has increased the understanding of wetlands' influence on the numbers of waterfowl that breed and their breeding success. However, the relation between wetlands and the population and propagation of various waterfowl species is not well understood.
This relation depends on: 1 the number of wetlands in the area; 2 the wetlands' size and water depth; 3 whether the wetlands hold open water in the early spring or through late August; 4 the climate; and 5 the species of bird and the bird's adaptations to wetlands.
In the prairie pothole region in the late 's, for example, as the number of wetlands in an area increased, populations of dabbling ducks increased, but at a ratio of less than fig. In the past 20 years, the duck-pothole ratio has decreased, possibly due to decreases in upland cover and increases in predation. Bellrose also found waterfowl densities and propagation to be related to the number of wetlands per square mile; generally, waterfowl densities and propagation increased as the number of wetlands increased.
However, he found that mallard production decreased when the number of wetlands exceeded 12 per square mile. Different waterfowl species adapt to different wetland types, inhabit different geographic areas, and nest at different times. The relation of many other species of birds to wetlands are undoubtedly just as complex. About one-third of North American bird species use wetlands for food, shelter, and or breeding Kroodsma, Thus, widespread draining and altering of wetlands has affected bird populations.
Because most of the wetland drainage and alteration occurred between the 's and , before scientific estimates of bird populations began, most estimates of population declines are inferred. Before the passage of the Migratory Bird Treaty Act in , the reduction in waterfowl populations was blamed largely on excessive hunting and wetland drainage Day, However, since most of the reduction has been attributed to the loss or degradation of wetlands Bellrose and Trudeau, and the loss of suitable upland habitats that surround wetlands.
For most wetland-dependent birds, habitat loss in breeding areas translates directly into population losses. As wetlands are destroyed, some birds may move to other less suitable habitats, but reproduction tends to be lower and mortality tends to be higher.
Hence, the birds that breed in these poorer quality habitats will not contribute to a sustainable population through the years Pulliam and Danielson, About one-half of the animals that are federally designated as endangered or threatened are wetland dependent Niering, Of these, 17 are bird species or subspecies table 5.
These birds are categorized as endangered or threatened because their populations are so low that the risk of their extinction is real and immediate. The circumstances that cause each species or subspecies to be endangered differ greatly. Water levels can be stabilized in wetlands that otherwise would undergo beneficial drawdowns or water-table fluctuations.
Wetland vegetation may be altered by harvesting or by introducing exotic species, making it of little or no value to wetland-dependent birds.
An example of wetland degradation is found in the Chesapeake Bay region. Nutrients and sediments entering the bay from agricultural, urban, and industrial areas have caused increased algal blooms, decreased invertebrate production, and lowered oxygen levels. This degradation has reduced the acreage of seagrasses that form an important link in the food chain for invertebrates, fish, and wetland-dependent birds. The decline in the canvasback duck population in this area is thought to be directly related to the decline in seagrasses.
Chemicals and sediments that move from agricultural areas into wetlands are two of the most pervasive sources of degradation. The shift in human populations from inland areas to coastal areas of the United States has caused problems in coastal wetlands through overloaded sewage treatment systems. The large and growing volume of industrial wastes that enter ground- and surface-water supplies also threatens to degrade wetlands.
These threats, combined with habitat destruction, have a net negative effect on the population of wetland birds. Thus, if the amount and quality of wetland habitat is substantially reduced, populations of wetland-dependent birds in the area also can be expected to decrease.
Fish and Wildlife Service, and by private organizations, such as the Nature Conservancy or the National Audubon Society, offers the best assurance that the highest value wetlands will be maintained for future generations.
A discussion of the agencies and organizations that participate in management and conservation of wetlands in each State can be found in the State Summaries section of this report.
A few early concerns for wetlands important to waterfowl are reflected in the creation of the first national wildlife refuge and in the establishment of the Federal Duck Stamp program.
The first national wildlife refuge was created in , by President Theodore Roosevelt, to protect a wetland--Pelican Island, Florida U.
Fish and Wildlife Service, []. Agricultural and forest land are being converted to commercial and residential development. Because of drainage and nonpoint source water pollution, many wetland and aquatic wildlife species have declined in this area. Wetlands and riparian areas support a higher diversity and abundance of wildlife species than other farmland habitats.
Landscape changes to this area have impacted the rate of wetland loss. Less than 60 percent of the original wetlands in the lower Atlantic Flyway still exist. And the remaining wetlands are declining in quality because of nutrient loading, altered hydrology, and urban encroachment.
Wetland wildlife species have experienced long-term declines. Loss and degradation of the south aquatic system and loss of much of the native fauna contribute to the decline of global biotic diversity. The loss and decreased quality of existing wetlands and associated upland buffers in areas such as, but not limited to, playas or seasonal depressional wetlands, saline lakes, and riparian corridors have resulted in declining wildlife populations.
Significant loss and degradation of Gulf Coast estuaries have occurred because of saltwater intrusion from canal construction and development, geologic subsidence, and developmental pressures along the coastal regions. The Playa Lake Joint Venture reports that protection and improvement of playas in the Southwest are vital to ensuring continued accommodation of waterfowl and other water birds overwintering in, migrating through, and breeding in this region.
At one time, open prairie wetlands accounted for nearly one-fourth of the total surface area of the Midwest. However, drainage for crop production has severely reduced wetland acreage. Most of the wetland acreage that remains is either forested or degraded. Nearly 60 percent of the rural land in this region is cropland and pasture.
Wetland drainage and alteration of associated uplands have led to declines in many wetland wildlife species. Population levels of certain species of waterfowl and other migratory birds are declining. The recreational and economic impacts of wetland loss in this area are a major concern.
This area, although one of the most altered ecosystems in the country, is still one of the most ecologically rich regions in the world.
When the most recent glacier retreated, it created the prairie potholes--areas containing a high density of isolated wetlands interspersed among the short and tall grass and mixed-grass prairies.
This unique combination of habitats supported the evolution of a great diversity of ground-nesting wildlife, particularly migratory birds. Prairie potholes are the most important breeding grounds for waterfowl in North America. Over the years, nearly half of the original wetlands in the prairie pothole region have been drained. Of those remaining, most are cropped when the weather permits. Agricultural practices around the potholes often result in sedimentation and addition of pesticides and fertilizers, resulting in degraded wetland vegetation, water quality, and wetland habitats.
Runoff from unprotected cropland is slowly filling many of these wetlands with sediment. Livestock grazing is the most prevalent agricultural use in this area. Fifty-nine percent of the original wetlands have been lost throughout the region. Losses of wetlands in arid areas are particularly detrimental to wildlife. Wetlands in California's Central Valley have been reduced from more than 4 million acres to about , acres.
The natural annual flood cycle of the remaining Central Valley wetlands was eliminated by flood control and water-development projects. Consequently, the wetlands must be managed by artificial and intentional flooding with scarce, expensive water. Seventy percent of these remaining wetlands are privately owned. The Beaver Creek Project in Clarion County, Pennsylvania, is a wetlands project that not only provides wildlife habitat, but also serves as a fisheries resource, offers recreational opportunities, and provides a natural setting for an outdoor learning center.
Nine small lakes have been built, totaling 70 acres. All the lakes have been stocked with bass and bluegill and produce a variety of aquatic plants such as wild celery, duck potato, and buttonrush.
These plants can be harvested and transplanted to other wetlands for wildlife food and to help restore water quality. Several waterfowl species have had great nesting success.
A larger lake will also be constructed for use as a water source for western Clarion County. A diversity of wetland community types provides essential stopover habitats for members of every bird group in Wisconsin. For more information, including great places to view migratory birds and suggestions of things you can do to support migrating birds, visit the Wisconsin Stopover Initiative website.
With increasing water depth 1. Wild rice stands with the right water depth serve as valuable stopover habitat for Wood Duck, Mallard, Redhead, Canvasback, and other migrant waterfowl. Additional priority stopover habitats for waterfowl include seasonally flooded basins acres in agricultural fields as well as hard water inland lakes and flowages greater than five acres in size.
Marshes provide abundant foraging opportunities for these migrant species. Mudflats and exposed shorelines of emergent marshes contain aquatic plants eaten by Sora, Virginia Rail, and Common Moorhen and aquatic invertebrates consumed by American Bittern, Virginia Rail, and King Rail.
Shallow water areas adjacent to mudflats are foraging areas for Great Egret, Snowy Egret, Green Heron, and Great Blue Heron, while open water zones surrounded by scattered emergent vegetation are important features for Pied-billed Grebes and Red-necked Grebes.
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